1. Field of the Invention
The present invention relates to a semiconductor dynamic sensor in which a displacement portion, having beam structure and being displaced in response to applied dynamic force, is formed in a semiconductor substrate to output a signal according to a displacement amount of the displacement portion. The present invention also relates to methods of transport and collet suction for the semiconductor dynamic sensor.
2. Description of Related Art
As an example of an acceleration sensor, a semiconductor acceleration sensor is disclosed in U.S. Pat. Ser. No. 2001/55836 A1 (JP-A-2002-5951). This semiconductor acceleration sensor includes a displacement portion comprising a fixed electrode and a movable electrode. Further, this sensor outputs a signal representing a change of capacitance between the fixed electrode and the movable electrode. This change of capacitance corresponds to a displacement amount of the movable electrode in response to an acceleration change. This sensor is mounted on a processing circuit chip.
FIG. 6 shows an example of the above semiconductor acceleration sensor. As shown in this figure, a displacement portion 4 is formed in a semiconductor acceleration sensor 1. The displacement portion 4 includes a fixed electrode 2 and a movable electrode 3. Each of the electrodes 2, 3 has beam structure and these electrodes 2, 3 face each other. Further, these electrodes 2, 3 are separated from each other and there is a clearance between them. Furthermore, a plurality of electrode pads 5–7 and a reference electrode pad 8 are formed on a surface of the semiconductor acceleration sensor 1. Each of the pads 5–7 corresponds to the fixed electrode 2 or the movable electrode 3. The reference electrode pad 8 is used for voltage reference. The pads 5–7 output a signal representing a capacitance which changes based on displacement of the movable electrode 3.
In the above semiconductor acceleration sensor 1, detection accuracy may deteriorate according to accuracy of a mounting position relative to a processing circuit chip. It is unstable if bonding material is used to fix the semiconductor acceleration sensor 1 on the processing circuit chip. Accordingly, an adhesive film 9 is stuck to a bottom surface of the semiconductor acceleration sensor 1 as shown in FIG. 7 before mounting on the circuit chip. Then, the semiconductor acceleration sensor 1 is sucked by a collet chuck and mounted on the processing circuit chip. The collet chuck is an apparatus for grasping objects. Here, it is supposed to be a type which grasps objects by air suction.
Recently, the semiconductor acceleration sensor 1, for example, is used for VSC (Vehicle Stability Control), and high sensitivity and high accuracy are desired in the semiconductor acceleration sensor 1. In order to realize this, it is necessary to further reduce elasticity of the adhesive film 9 sticking to the semiconductor acceleration sensor 1.
However, it is difficult to stick an adhesive film 9 with low elasticity to the bottom surface of the semiconductor acceleration sensor 1 before mounting. Accordingly, the adhesive film 9 with low elasticity is stuck to the processing circuit tip in advance, and the semiconductor acceleration sensor 1 is mounted. That is, there is no adhesive film 9 on the bottom surface of the semiconductor acceleration sensor 1 before mounting. In addition, the displacement portion 4 of the semiconductor acceleration sensor 1 is easy to be displaced in response to slight acceleration because of its high response characteristic. Therefore, air is sucked from a clearance between the fixed electrode 2 and the movable electrode 3 when a collet chuck 10 sucks the semiconductor acceleration sensor 1. As a result, as shown in FIG. 8, the displacement portion 4 may be damaged.